This invention relates to data communications devices such as modems. Data communications devices, such as modems, multiplexers, and digital service units, are generally well known in the art. These devices are typically used to transmit digital data signals from one computer to another using telephone lines or other communications channels.
Data communications devices or modems frequently include microprocessors that enable them to perform other functions in addition to their data communications function. Many of these data communications devices include the ability to run diagnostic tests on internal circuitry to identify when a fault has developed. Many have the ability to perform a so-called local loop-back test wherein the device accepts data from a DTE device (such as a computer or computer data terminal) connected to a DTE port, sends the data through the data communications device and returns it back to the DTE device, which compares the data returned from the modem to the data sent into the modem. In such a local loop back test, if the data returned from the modem matches the data sent, the modem may be assumed to be working properly.
In addition to local loop-back tests, many data communications devices also include the capability of testing at least portions of a distant data communications device that it is communicating with by instructing the far-end device to enter a remote loop-back test mode and thereafter sending test information from the near end communications device to the far-end data communications device, which loops the test data back to the sending device. In such a far end loop-back test, if the data returned by the far end matches the data sent, it can reasonably be assumed that the communications channel and the modems or data communications devices are both working properly.
Even though many of these data communications devices include the capability of testing themselves locally, as well as testing a far-end device remotely, running these tests typically requires the interaction of an operator who must initiate the test via a DTE at one end of a communications loop. (A communications loop can be considered to be comprised of data communications devices coupled together through a telephone link or other communications channel.) In a large distributed communications network which might have hundreds of modems or data communications devices, any one of which is capable of communicating with other modems of the network, running such manually controlled tests on each modem is a labor-intensive task.
A data communications device or modem for coupling a DTE device to a communications channel that is testable under the control and direction of a single central computer would be an improvement over the prior art in that it would reduce the required operator intervention. A data network of communications devices that are testable by a computer from one central location would also be an improvement over the prior art.